The long-term goal of this research is to attain a better understanding of the cause of neurodegeneration in multiple sclerosis (MS). This is particularly important to US Veterans, who develop a disproportionate share of progressive MS; the type of MS in which neurodegeneration predominates. Considering there are no treatments for progressive MS that specifically impede or reverse neurodegeneration, understanding mechanisms of neurodegeneration is crucial to developing novel treatments for progressive MS. We believe we have discovered a novel mechanism related to `dying back' axonal degeneration, a feature of neurodegeneration present in the central nervous system (CNS) of MS patients. Our data indicates that an RNA binding protein, heterogeneous nuclear ribonuclear protein A1 (hnRNP A1), contributes to neurodegeneration in MS. Dysfunctional RNA binding proteins, including hnRNP A1, have been found to cause amyotrophic lateral sclerosis (ALS), dementia and other chronic neurodegenerative diseases. Yet the role of RNA binding proteins such as hnRNP A1 in the pathogenesis of immune mediated disorders of the CNS remains largely unknown. MS patients develop antibodies to the `M9' sequence of hnRNP A1. M9 is required for transport of hnRNP A1 into and out of the nucleus to the cytoplasm. Exposure of neuronal cell lines to anti- hnRNP A1 A1-M9 antibodies (whose epitope overlaps the immunodominant epitope of IgG isolated from MS patients), resulted in the anti-M9 antibodies entering neurons, which in turn, caused mislocalization of hnRNP A1 from the nucleus to the cytoplasm, stress granule formation and apoptosis. hnRNP A1 mislocalization and stress granule formation are markers of neurodegeneration. In addition, in an animal model of MS, anti-M9 antibodies worsened disease, changed clinical disease phenotype from flaccid to spastic, and caused neurodegeneration of specific tracts of the CNS consistent with `dying back' axonal degeneration. Further, we discovered there are genomic DNA mutations in hnRNP A1 isolated from the lymphocytes of MS patients. Like anti-hnRNP A1-M9 antibodies, transfection of mutant forms of hnRNP A1 caused mislocalization of hnRNP A1 protein and apoptosis in neuronal cell lines. Taken together, these data indicate that autoimmunity to and DNA mutations within hnRNP A1 contribute to neurodegeneration in MS. The objectives of this proposal are to determine how DNA mutations, pro-inflammatory cytokines and anti-M9 autoantibodies contribute to the molecular dysfunction of hnRNP A1 and the resulting neuronal and axonal degeneration in immune-mediated disease of the central nervous system. In this grant we will: 1. Determine the contribution of hnRNP A1 genomic DNA mutations to neurodegeneration in MS brains. 2. Examine mechanisms by which pro-inflammatory cytokines and anti-hnRNP A1-M9 antibodies cause neurodegeneration in primary neurons. 3. Examine mechanisms by which pro-inflammatory cytokines and anti-hnRNP A1-M9 antibodies cause neurodegeneration, including `dying back' axonal degeneration of specific neural pathways in an animal model of MS